An asynchronous rectification type switching power supply device X (of a step-up type shown in FIG. 15) has been conventionally used as a power supply device for various applications.
However, such an asynchronous rectification type switching power supply device X does not have the sink current capability (the capability of autonomously extracting electric charges of an output capacitor CX) on its circuit configuration. Therefore, when an output voltage Vo is to be gradually decreased within a predetermined time, it is necessary to provide a separate discharging circuit, which causes a problem of an output ripple (see FIG. 16) or heat generation at the time of the operation of the discharging circuit.
This problem is not limited to the asynchronous rectification type switching power supply device but may be applied to a synchronous rectification type switching power supply device with a light load mode (a function being operated in a discontinuous current mode by cutting off a reverse current in the case of a light load).